In many localities a plurality of radio frequency channels are allocated for use by either mobile or portable radio transceivers. As used herein, examples described identifying mobile radios are equally applicable to portable radios and vice versa. Each of the radio channels used by mobile or portable radio units usually includes at least two separate and distinct frequencies, one for transmitting and one for receiving. Generally, there may be, and usually are, many more mobile radio transceivers than there are available radio channels in a given locality.
Consequently, some arrangement is needed for sharing available spectrum space among users. One such arrangement enables a mobile radio transceiver user to obtain access to a radio channel that is not in use (without disturbing the privacy of channels already in use) and to thereafter establish communication with one or more specifically designated mobile transceivers over that acquired radio frequency. When the user is finished using the channel, the user relinquishes it for use by other mobile transceivers.
One such system for establishing communication between mobile radio transceivers using a repeater system over a radio frequency channel selected from a plurality of such channels is disclosed in commonly assigned U.S. Pat. No 4,360,927 to Bowen et al issued Nov. 23, 1982, which U.S. Patent is expressly incorporated herein by reference. Such a repeater system is utilized to route signals for rebroadcast to receiving mobiles since direct mobile-to-mobile radio communications are limited in range by low antenna heights and relatively low power.
Many diverse groups of mobile users in the same community utilize the same repeater system by transmitting and receiving on the appropriate frequencies. In general, the type of communication on a community repeater is a push-to-talk, release-to-listen message transmission of short duration in between one mobile user and a group of at least one other mobile user.
Trunked radio repeater systems offer better control of communications by being automatically trunked on a plurality of communication channels. Mobile or portable users in such a system must request service from a controller and receive a channel assignment and permission to transmit from the controller before being allowed to transmit on one of the channels. In such a trunked radio system, a calling unit initiates a call by, for example, depressing a push-to-talk control switch. The depression of the push-to-talk control switch in addition to "waking up" the transceiver microprocessor associated with the calling unit additionally serves to inform a system controller associated with the repeater system that a calling unit is requesting service. The system controller searches for an available channel. If a channel is available, both the calling unit and the called units are informed as to the operating or working channel which has been automatically assigned to handle the transmission between units. The channel service request message to the system controller and the message from the system controller to the mobile units relating to the working channel assignment occur over a control channel.
In such trunked radio repeater systems, if the system controller determines that a request for channel assignment is made at a time when all channels are busy, demands for service on the system are placed in a queue (e.g., a memory device associated with the system controller which stores indicia relating to the service request). The calling unit is informed, for example, by a digital message transmitted over the control channel that all channels are currently busy and that it has been placed in the queue of callers requesting service. As operational or working channels become available, these channels are assigned to calling units from the queue of callers requesting service but which were unserved at the time of request due to the system being busy.
In trunked radio systems, mobile units have heretofore been grouped into formalized related fleets. Each of the units in a fleet may, for example, have associated coding schemes such as continuous subaudible signals or digital signals which are transmitted by a mobile in the fleet to activate otherwise muted receivers of other members of its fleet. In this manner, a mobile user no longer has to monitor every message on the channel.
Heretofore, in a trunked radio system where mobile units are grouped into fleets, when all channels are busy, the calling unit is transmitted, for example, a digital message over the control channel to indicate that it has been placed in the queue of callers requesting service. The present invention recognizes that there is a dire need, not only to inform the calling unit that it has been placed in queue, but also to inform all units in the fleet that a call initiating unit has been placed in queue.
As will be appreciated by those familiar with the portable or mobile radio communications art, transmissions often involve messages relating to emergency or other public interest related communications. Additionally, a calling unit associated with a fleet dedicated to a particular business enterprise from time to time transmits a messages of critical importance to the enterprise. For example, a calling unit may need to redirect other members of the fleet to a location in the community where representatives of the enterprise are required to be present.
In accordance with the present invention, not only is the initiating or calling unit provided with an indication that all channels are busy and that it has been placed in queue, but also the called units in the respective called fleet are given an indication that in effect they have been placed in queue. This indication may, for example be an audible indication and/or a visual indication from a display lamp, light emitting diode or liquid crystal display.
In this fashion, each mobile or portable radio in a fleet is provided with advance notice that it is about to receive a call momentarily. In this regard, such a mobile or portable radio is informed that as soon as the system can provide a channel assignment for the calling unit, that a call will be received. Accordingly, a member of the fleet receiving such advance notice, rather than leaving his or her vehicle or turning off his or her radio to, for example, take an extended break, will be informed to standby the radio since a call is imminent.
In this fashion, the present invention enhances the probability that an emergency call, which may have life and death consequences (or an important business call) will be received and responded to rather than go unanswered. This advance notice of an impending communication for a particular group or fleet of a trunked radio system places all units receiving the queue indication in the "be ready to receive a radio call" status.
The fleet queue alert thereby notifies all units in the fleet that one unit in the fleet has requested service on the system, found the system "busy", and has been placed in a queue for assignment of a communications channels as soon as the system load, including previously queued units, permits.
In addition to placing all units of a fleet receiving the queue indication in a "be ready to receive radio call" state, the present invention also contemplates use in conjunction with a telephone interconnection network where a telephone call via an interconnected landline is attempted to be placed with a mobile or portable radio. In this embodiment, a called (individual) mobile or portable radio user is alerted that he or she is about to receive a landline to mobile call.